Mineral magnetism of shocked ferrimagnetic minerals
Final Report Abstract
Meteorite impact structures have a strong effect on planetary magnetic anomalies. The effects of shock waves on intrinsic magnetic properties of minerals and rocks are therefore essential for the understanding of magnetization processes and magnetic field anomalies related to impact structures on Earth and other planetary bodies. This project combined rock magnetic measurements with microstructural studies in a shocked magnetite-bearing ore, in impacted and non-impacted volcanic rocks of the El’gygytgyn impact structure, Russia, and of cohenite from the Morasko iron meteorite, Poland. During this study, a serie of striking and up to now not well-constrained magnetic features for magnetic material under extreme conditions were observed: The transition from multidomain to pseudo-single magnetic domain state in shocked magnetite is controlled by lattice defects like shear bands, twin lamellae and amorphous regions, which can be (partially) annealed by short-term heating. This observation might be crucial for the understanding of formation mechanisms of magnetic anomalies in large impact craters. - Cohenite, an important mineral in shocked iron meteorites, recovers its magnetic domain state even after heating to 700 °C because the magnetic domains are controlled by a strong crystal anisotropy. This observation suggests that this magnetic mineral might be a good recorder of magnetic fields in planetary core material. This research significantly contributes to the understanding of pre-, syn- and post-impact induced features, which was shown by the comparison of our experimental results with shocked natural material of the El’gygytgyn impact structure. Overall, shock waves significantly reduce the magnetic susceptibility and therefore the induced magnetization of impacted rocks. Further studies related to the post-shock heating history of impact structures are needed to understand the complex magnetic signatures of impact structures, especially on Earth.
Publications
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2016. Cohenite - a stable magnetic carrier in iron meteorites. The IRM (Institute for Rock Magnetism) Quarterly, Spring 2016, Vol. 26, No. 1, p.2-3
Reznik, B., Kontny, A.
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2016. Effect of shock waves on magnetic susceptibility and microstructure of a magnetite-bearing ore”, Meteoritics & Planetary Science
Reznik, B., Kontny, A., Fritz, J.
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2016. Shock-induced deformation phenomena in magnetite and their consequences on magnetic properties. Geochemistry, Geophysics, Geosystems, 17
Reznik, B., Kontny, A., Fritz, J., Gerhards, U.
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Magnetic domains and thermomagnetic stability of cohenite from the Morasko iron meteorite. Magnetism and Magnetic Materials
Reznik, B., Kontny, A., Uehara, M., Gattacceca, J., Solheid, P., Jackson, M.
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2017. Effect of shock pressure and temperature on titanomagnetite from ICDP cores and target rocks of the El’gygytgyn impact structure, Russia. Studia Geophysica et Geodaetica, 61, 162-183
Kontny, A., Grothaus, L.
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2018. Post-shock thermally induced transformations in experimentally shocked magnetite. Geochemistry, Geophysics, Geosystems
Kontny, A., Reznik, B., Boubnov, A., Göttlicher, J., Steininger, R.
